This invention relates to a transmitter for a fiber optics communication system, and more particularly a transmitter employing a combination of a semiconductor light source and semiconductor optical amplifier.
A semiconductor optical amplifier may be the same as a semiconductor laser, except for the range of electrical inputs and light outputs in which the device is operated. This type is called a Fabry-Perot amplifier. The other type is the so-called traveling-wave amplifier. The optical amplifier receives a light input, and it has an electrical current input which is not large enough to cause lasing. In the appropriate operation range, the amplifier provides an amplified light output which varies in relation to the electrical current and in relation to the light input.
The amplification provided by an optical amplifier is largest when light input is smallest. Accordingly, such amplifiers have come to be used at the receiving end of a fiber optics communication link, where the optical power in the fiber has been attenuated by the transmission. In such applications, the amplifier can provide a relatively large gain factor, such as 50. At the light power levels emitted by a laser or LED at the transmission end of a fiber optic link, the amplifier can only be expected to provide a gain in the range of 2 to 3. Thus, amplifiers have not been used at the transmitting end of such communication systems.